Multi-speed power transmissions having two or more axes generally extend the shaft members on at least two of the axes in the longitudinal direction of the transmission in order to obtain multiple speed ratios between the shafts. In order to increase the total number of speed ratios, the longitudinal dimension of the transmission increases.
In transverse front wheel drive transmissions, the longitudinal dimension of the transmission is limited by the available tread width and a maximum allowable angle of the drive axles. In passenger type vehicles, this limits the number of ratios available. Also, in countershaft or parallel shaft type transmissions, a ratio using a one-way clutch is generally limited to the first or lowest forward speed ratio.
In some farm tractor type applications, where ground clearance is abundant, the transmission gearing can be assembled on plural parallel shafts with one shaft being an input shaft and other of the shafts being interconnected therewith by gearing. These transmissions cascade the gear ratios, that is, they utilize gears on more than two shafts to establish some of the gear ratios in the transmission. Quite often, these transmissions utilize the same series or a portion thereof for various gear ratios. These transmissions are generally designed to provide a maximum number of close ratio gear steps, such that the operating performance of the tractor will be closely controlled. This number and closeness of gear ratios is not acceptable for passenger type vehicles. Most automobile transmissions are designed to provide four to six forward gear ratios and a reverse gear ratio.